Previous work in our laboratory has revealed an unexpected and paradoxical effect of combined NGF and 6-hydroxydopamine (6-OHDA) treatment on sympathetic ganglia in infant mice. While NGF alone stimulates ganglion growth and 6-OHDA is neurotoxic, following simultaneous administration ganglia were found to be larger than after NGF treatment alone. Currently, combined electron microscopic, histological, and biochemical studies of this phenomenon are being carried out and additional agents known to interact with the sympathetic system are being tested for their effects when administered with NGF. In addition, possible effects of centrally applied NGF are being investigated with Falck-Hillarp, immunofluorescence, and electron microscopic methods. Although no such direct effects have been discovered to date, it has been found that in infant rats centrally administered NGF may induce the formation of massive adrenergic fiber systems with the CNS which arise from peripheral sympathetic ganglia. The exact sites of termination of this system are now under study. Finally, the normal anatomy of the central adrenergic system is being thoroughly examined with a highly sensitive immunofluorescence method utilizing dopamine-B-hydroxylase, and murine choline acetyltransferase is being purified for use with this same technique.